Patterns of CAG repeat instability in the central nervous system and periphery in Huntington's disease and in spinocerebellar ataxia type 1

The expanded HTT CAG repeat causing Huntington’s disease (HD) exhibits somatic expansion proposed to drive the rate of disease onset by eliciting a pathological process that ultimately claims vulnerable cells. To gain insight into somatic expansion in humans, we performed comprehensive quantitative analyses of CAG expansion in ~50 central nervous system (CNS) and peripheral postmortem tissues from seven adult-onset and one juvenile-onset HD individual. We also assessed ATXN1 CAG repeat expansion in brain regions of an individual with a neurologically and pathologically distinct repeat expansion disorder, spinocerebellar ataxia type 1 (SCA1). Our findings reveal similar profiles of tissue instability in all HD individuals, which, notably, were also apparent in the SCA1 individual. CAG expansion was observed in all tissues, but to different degrees, with multiple cortical regions and neostriatum tending to have the greatest instability in the CNS, and liver in the periphery. These patterns indicate different propensities for CAG expansion contributed by disease locus-independent trans-factors and demonstrate that expansion per se is not sufficient to cause cell type or disease-specific pathology. Rather, pathology may reflect distinct toxic processes triggered by different repeat lengths across cell types and diseases. We also find that the HTT CAG length-dependent expansion propensity of an individual is reflected in all tissues and in cerebrospinal fluid. Our data indicate that peripheral cells may be a useful source to measure CAG expansion in biomarker assays for therapeutic efforts, prompting efforts to dissect underlying mechanisms of expansion that may differ between the brain and periphery.

Reelin signaling modulates GABAB receptor function in the neocortex

Reelin is a protein that is best known for its role in controlling neuronal layer formation in the developing cortex. Here, we studied its role for post-natal cortical network function, which is poorly explored. To preclude early cortical migration defects caused by Reelin deficiency, we used a conditional Reelin knock-out (RelncKO ) mouse, and induced Reelin deficiency post-natally. Induced Reelin deficiency caused hyperexcitability of the neocortical network in vitro and ex vivo. Blocking Reelin binding to its receptors ApoER2 and VLDLR resulted in a similar effect. Hyperexcitability in RelncKO organotypic slice cultures could be rescued by co-culture with wild-type organotypic slice cultures. Moreover, the GABAB receptor (GABAB R) agonist baclofen failed to activate and the antagonist CGP35348 failed to block GABAB Rs in RelncKO mice. Immunolabeling of RelncKO cortical slices revealed a reduction in GABAB R1 and GABAB R2 surface expression at the plasma membrane and western blot of RelncKO cortical tissue revealed decreased phosphorylation of the GABAB R2 subunit at serine 892 and increased phosphorylation at serine 783, reflecting receptor deactivation and proteolysis. These data show a role of Reelin in controlling early network activity, by modulating GABAB R function. Cover Image for this issue: https://doi.org/10.1111/jnc.15054.

Postnatal Developmental Expression Profile Classifies the Indusium Griseum as a Distinct Subfield of the Hippocampal Formation

The indusium griseum (IG) is a cortical structure overlying the corpus callosum along its anterior–posterior extent. It has been classified either as a vestige of the hippocampus or as an extension of the dentate gyrus via the fasciola cinerea, but its attribution to a specific hippocampal subregion is still under debate. To specify the identity of IG neurons more precisely, we investigated the spatiotemporal expression of calbindin, secretagogin, Necab2, PCP4, and Prox1 in the postnatal mouse IG, fasciola cinerea, and hippocampus. We identified the calcium-binding protein Necab2 as a first reliable marker for the IG and fasciola cinerea throughout postnatal development into adulthood. In contrast, calbindin, secretagogin, and PCP4 were expressed each with a different individual time course during maturation, and at no time point, IG or fasciola cinerea principal neurons expressed Prox1, a transcription factor known to define dentate granule cell fate. Concordantly, in a transgenic mouse line expressing enhanced green fluorescent protein (eGFP) in dentate granule cells, neurons of IG and fasciola cinerea were eGFP-negative. Our findings preclude that IG neurons represent dentate granule cells, as earlier hypothesized, and strongly support the view that the IG is an own hippocampal subfield composed of a distinct neuronal population.

A protein quality control pathway regulated by linear ubiquitination

Neurodegenerative diseases are characterized by the accumulation of misfolded proteins in the brain. Insights into protein quality control mechanisms to prevent neuronal dysfunction and cell death are crucial in developing causal therapies. Here, we report that various disease-associated protein aggregates are modified by the linear ubiquitin chain assembly complex (LUBAC). HOIP, the catalytic component of LUBAC, is recruited to misfolded Huntingtin in a p97/VCP-dependent manner, resulting in the assembly of linear polyubiquitin. As a consequence, the interactive surface of misfolded Huntingtin species is shielded from unwanted interactions, for example with the low complexity sequence domain-containing transcription factor Sp1, and proteasomal degradation of misfolded Huntingtin is facilitated. Notably, all three core LUBAC components are transcriptionally regulated by Sp1, linking defective LUBAC expression to Huntington's disease. In support of a protective activity of linear ubiquitination, silencing of OTULIN, a deubiquitinase with unique specificity for linear polyubiquitin, decreases proteotoxicity, whereas silencing of HOIP has the opposite effect. These findings identify linear ubiquitination as a protein quality control mechanism and hence a novel target for disease-modifying strategies in proteinopathies.

Neurodegeneration in the olfactory bulb and olfactory deficits in the Ccdc66 -/- mouse model for retinal degeneration

The Ccdc66-deficient (Ccdc66 -/-) mouse model exhibits slow progressive retinal degeneration. It is unclear whether CCDC66 protein also plays a role in the wildtype (WT; Ccdc66 +/+) mouse brain and whether the lack of Ccdc66 gene expression in the Ccdc66 -/- mouse brain may result in morphological and behavioral alterations. CCDC66 protein expression in different brain regions of the adult WT mouse and in whole brain during postnatal development was quantified by SDS-PAGE and Western blot. Ccdc66 reporter gene expression was visualized by X-gal staining. Selected brain regions were further analyzed by light and electron microscopy. In order to correlate anatomical with behavioral data, an olfactory habituation/dishabituation test was performed. CCDC66 protein was expressed throughout the early postnatal development in the WT mouse brain. In adult mice, the main olfactory bulb exhibited high CCDC66 protein levels comparable to the expression in the retina. Additionally, the Ccdc66 -/- mouse brain showed robust Ccdc66 reporter gene expression especially in adult olfactory bulb glomeruli, the olfactory nerve layer and the olfactory epithelium. Degeneration was detected in the Ccdc66 -/- olfactory bulb glomeruli at advanced age. This degeneration was also reflected in behavioral alterations; compared to the WT, Ccdc66 -/- mice spent significantly less time sniffing at the initial presentation of unknown, neutral odors and barely responded to social odors. Ccdc66 -/- mice develop substantial olfactory nerve fiber degeneration and alteration of olfaction-related behavior at advanced age. Thus, the Ccdc66 -/- mouse model for retinal degeneration adds the possibility to study mechanisms of central nervous system degeneration.

Exome Sequencing Reveals AGBL5 as Novel Candidate Gene and Additional Variants for Retinitis Pigmentosa in Five Turkish Families

PURPOSE

Retinitis pigmentosa (RP) is the most common inherited retinal disease with high genetic heterogeneity and variable phenotypes. Characteristic symptoms include night blindness and progressive loss of visual field, leading to blindness. Mutations in >60 genes have been identified to date as causative for RP, and additional candidate genes are assumed.

METHODS

To find the disease-causing mutations in the affected members of five Turkish families, we sequenced whole exomes using an Illumina platform.

RESULTS

Among all candidate genes for retinal degeneration we found two previously known sequence variations: a 4 bp deletion in the RPGR gene (c.1662_1665delAGAA; p.Glu555Glyfs*14) and a recently described USH1-causing missense mutation in MYO7A (c.472G>A, p.Gly158Arg). Furthermore, a novel 1 bp deletion in the VCAN gene (c.5118delA; p.Ser1707Valfs*44) was detected as well as a large deletion in EYS, spanning ∼ 400kb and comprising exons 16-26 (p.fs*). In one family, exome analyses of two affected individuals revealed a homozygous missense mutation (c.883G>A; p.Asp295Asn) in the AGBL5 (Agbl5; CCP5) gene, previously not reported to be associated with RP. RNA and protein analyses showed expression in human retina, as well as in mouse retina, brain and testis. Furthermore, cDNA analyses indicate the existence of tissue-specific AGBL5 splice variations in humans. AGBL5/CCP5 immunoreactivity was also visualized in human and mouse retinae.

CONCLUSION

Due to the characteristic RP phenotype in patients carrying the AGBL5 missense mutation we suggest this gene as a candidate for a new form of autosomal recessively inherited RP and recommend further investigation to confirm this hypothesis.

Association of variation in the LAMA3 gene, encoding the alpha-chain of laminin 5, with atopic dermatitis in a German case-control cohort

BACKGROUND

Atopic dermatitis (AD) is a chronic inflammatory skin disorder caused by complex interaction of genetic and environmental factors. Besides mutations in the filaggrin gene, leading to impaired skin barrier function, variation in genes encoding additional skin proteins has been suggested to contribute to disease risk. Laminin 5, playing an important role in skin integrity, is composed of three subunits encoded by the LAMA3, LAMB3 and LAMC2 genes in which biallelic mutations cause epidermolysis bullosa junctionalis. We aimed at evaluating the role of variation in the LAMA3, LAMB3 and LAMC2 genes for AD pathogenesis.

METHODS

29 single nucleotide polymorphisms (SNPs) were genotyped in the three genes in a German AD case-control cohort comprising 470 unrelated AD patients and 320 non-atopic controls by means of restriction enzyme digestion. Allele, genotype and haplotype frequencies were compared between cases and controls using chi-square testing and the Haploview software.

RESULTS

Several SNPs in the LAMA3 gene showed significant association with AD in our cohort (p <0.01), while we did not detect association with variations in the LAMB3 and LAMC2 genes. Haplotype analysis additionally revealed several significantly associated haplotypes in the LAMA3 gene. Due to extensive linkage disequilibrium, though, we were not able to further differentiate the specific disease causing variation(s) in this region.

CONCLUSIONS

We established the LAMA3 gene as novel potential susceptibility gene for AD. Additional studies in independent cohorts are needed to replicate these results.

SOX9 duplication linked to intersex in deer

A complex network of genes determines sex in mammals. Here, we studied a European roe deer with an intersex phenotype that was consistent with a XY genotype with incomplete male-determination. Whole genome sequencing and quantitative real-time PCR analyses revealed a triple dose of the SOX9 gene, allowing insights into a new genetic defect in a wild animal.

Inactivation of ceramide synthase 6 in mice results in an altered sphingolipid metabolism and behavioral abnormalities

The N-acyl chain length of ceramides is determined by the specificity of different ceramide synthases (CerS). The CerS family in mammals consists of six members with different substrate specificities and expression patterns. We have generated and characterized a mouse line harboring an enzymatically inactive ceramide synthase 6 (CerS6KO) gene and lacz reporter cDNA coding for β-galactosidase directed by the CerS6 promoter. These mice display a decrease in C16:0 containing sphingolipids. Relative to wild type tissues the amount of C16:0 containing sphingomyelin in kidney is ∼35%, whereas we find a reduction of C16:0 ceramide content in the small intestine to about 25%. The CerS6KO mice show behavioral abnormalities including a clasping abnormality of their hind limbs and a habituation deficit. LacZ reporter expression in the brain reveals CerS6 expression in hippocampus, cortex, and the Purkinje cell layer of the cerebellum. Using newly developed antibodies that specifically recognize the CerS6 protein we show that the endogenous CerS6 protein is N-glycosylated and expressed in several tissues of mice, mainly kidney, small and large intestine, and brain.

A novel transgenic rat model for spinocerebellar ataxia type 17 recapitulates neuropathological changes and supplies in vivo imaging biomarkers

Spinocerebellar ataxia 17 (SCA17) is an autosomal-dominant, late-onset neurodegenerative disorder caused by an expanded polyglutamine (polyQ) repeat in the TATA-box-binding protein (TBP). To further investigate this devastating disease, we sought to create a first transgenic rat model for SCA17 that carries a full human cDNA fragment of the TBP gene with 64 CAA/CAG repeats (TBPQ64). In line with previous observations in mouse models for SCA17, TBPQ64 rats show a severe neurological phenotype including ataxia, impairment of postural reflexes, and hyperactivity in early stages followed by reduced activity, loss of body weight, and early death. Neuropathologically, the severe phenotype of SCA17 rats was associated with neuronal loss, particularly in the cerebellum. Degeneration of Purkinje, basket, and stellate cells, changes in the morphology of the dendrites, nuclear TBP-positive immunoreactivity, and axonal torpedos were readily found by light and electron microscopy. While some of these changes are well recapitulated in existing mouse models for SCA17, we provide evidence that some crucial characteristics of SCA17 are better mirrored in TBPQ64 rats. Thus, this SCA17 model represents a valuable tool to pursue experimentation and therapeutic approaches that may be difficult or impossible to perform with SCA17 transgenic mice. We show for the first time positron emission tomography (PET) and diffusion tensor imaging (DTI) data of a SCA animal model that replicate recent PET studies in human SCA17 patients. Our results also confirm that DTI are potentially useful correlates of neuropathological changes in TBPQ64 rats and raise hope that DTI imaging could provide a biomarker for SCA17 patients.

Postsynaptic NO/cGMP increases NMDA receptor currents via hyperpolarization-activated cyclic nucleotide-gated channels in the hippocampus

The nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling cascade participates in the modulation of synaptic transmission. The effects of NO are mediated by the NO-sensitive cGMP-forming guanylyl cyclases (NO-GCs), which exist in 2 isoforms with indistinguishable regulatory properties. The lack of long-term potentiation (LTP) in knock-out (KO) mice deficient in either one of the NO-GC isoforms indicates the contribution of both NO-GCs to LTP. Recently, we showed that the NO-GC1 isoform is located presynaptically in glutamatergic neurons and increases the glutamate release via hyperpolarization-activated cyclic nucleotide (HCN)-gated channels in the hippocampus. Electrophysiological analysis of hippocampal CA1 neurons in whole-cell recordings revealed a reduction of HCN currents and a hyperpolarizing shift of the activation curve in the NO-GC2 KOs associated with reduced resting membrane potentials. These features were mimicked in wild-type (WT) neurons with an NO-GC inhibitor. Analysis of glutamate receptors revealed a cGMP-dependent reduction of NMDA receptor currents in the NO-GC2 KO mice, which was mimicked in WT by HCN channel inhibition. Lowering extracellular Mg(2+) increased NMDA receptor currents in the NO-GC2 KO and allowed the induction of LTP that was absent at physiological Mg(2+). In sum, our data indicate that postsynaptic cGMP increases the N-methyl-D-aspartate (NMDA) receptor current by gating HCN channels and thereby is required for LTP.

Pannexin1 stabilizes synaptic plasticity and is needed for learning

Pannexin 1 (Panx1) represents a class of vertebrate membrane channels, bearing significant sequence homology with the invertebrate gap junction proteins, the innexins and more distant similarities in the membrane topologies and pharmacological sensitivities with gap junction proteins of the connexin family. In the nervous system, cooperation among pannexin channels, adenosine receptors, and K_ATP channels modulating neuronal excitability via ATP and adenosine has been recognized, but little is known about the significance in vivo. However, the localization of Panx1 at postsynaptic sites in hippocampal neurons and astrocytes in close proximity together with the fundamental role of ATP and adenosine for CNS metabolism and cell signaling underscore the potential relevance of this channel to synaptic plasticity and higher brain functions. Here, we report increased excitability and potently enhanced early and persistent LTP responses in the CA1 region of acute slice preparations from adult Panx1^−/− mice. Adenosine application and N-methyl-D-aspartate receptor (NMDAR)-blocking normalized this phenotype, suggesting that absence of Panx1 causes chronic extracellular ATP/adenosine depletion, thus facilitating postsynaptic NMDAR activation. Compensatory transcriptional up-regulation of metabotropic glutamate receptor 4 (grm4) accompanies these adaptive changes. The physiological modification, promoted by loss of Panx1, led to distinct behavioral alterations, enhancing anxiety and impairing object recognition and spatial learning in Panx1^−/− mice. We conclude that ATP release through Panx1 channels plays a critical role in maintaining synaptic strength and plasticity in CA1 neurons of the adult hippocampus. This result provides the rationale for in-depth analysis of Panx1 function and adenosine based therapies in CNS disorders.

Selective hippocampal neurodegeneration in transgenic mice expressing small amounts of truncated Aβ is induced by pyroglutamate-Aβ formation

Posttranslational amyloid-β (Aβ) modification is considered to play an important role in Alzheimer's disease (AD) etiology. An N-terminally modified Aβ species, pyroglutamate-amyloid-β (pE3-Aβ), has been described as a major constituent of Aβ deposits specific to human AD but absent in normal aging. Formed via cyclization of truncated Aβ species by glutaminyl cyclase (QC; QPCT) and/or its isoenzyme (isoQC; QPCTL), pE3-Aβ aggregates rapidly and is known to seed additional Aβ aggregation. To directly investigate pE3-Aβ toxicity in vivo, we generated and characterized transgenic TBA2.1 and TBA2.2 mice, which express truncated mutant human Aβ. Along with a rapidly developing behavioral phenotype, these mice showed progressively accumulating Aβ and pE3-Aβ deposits in brain regions of neuronal loss, impaired long-term potentiation, microglial activation, and astrocytosis. Illustrating a threshold for pE3-Aβ neurotoxicity, this phenotype was not found in heterozygous animals but in homozygous TBA2.1 or double-heterozygous TBA2.1/2.2 animals only. A significant amount of pE3-Aβ formation was shown to be QC-dependent, because crossbreeding of TBA2.1 with QC knock-out, but not isoQC knock-out, mice significantly reduced pE3-Aβ levels. Hence, lowering the rate of QC-dependent posttranslational pE3-Aβ formation can, in turn, lower the amount of neurotoxic Aβ species in AD.

Ccdc66 null mutation causes retinal degeneration and dysfunction

Retinitis pigmentosa (RP) is a group of human retinal disorders, with more than 100 genes involved in retinal degeneration. Canine and murine models are useful for investigating human RP based on known, naturally occurring mutations. In Schapendoes dogs, for example, a mutation in the CCDC66 gene has been shown to cause autosomal recessively inherited, generalized progressive retinal atrophy (gPRA), the canine counterpart to RP. Here, a novel mouse model with a disrupted Ccdc66 gene was investigated to reveal the function of protein CCDC66 and the pathogenesis of this form of gPRA. Homozygous Ccdc66 mutant mice lack retinal Ccdc66 RNA and protein expression. Light and electron microscopy reveal an initial degeneration of photoreceptors already at 13 days of age, followed by a slow, progressive retinal degeneration over months. Retinal dysfunction causes reduced scotopic a-wave amplitudes, declining from 1 to 7 months of age as well as an early reduction of the photopic b-wave at 1 month, improving slightly at 7 months, as evidenced by electroretinography. In the retina of the wild-type (WT) mouse, protein CCDC66 is present at highest levels after birth, followed by a decline until adulthood, suggesting a crucial role in early development. Protein CCDC66 is expressed predominantly in the developing rod outer segments as confirmed by subcellular analyses. These findings illustrate that the lack of protein CCDC66 causes early, slow progressive rod-cone dysplasia in the novel Ccdc66 mutant mouse model, thus providing a sound foundation for the development of therapeutic strategies.

Efficacy of fumaric acid esters in the R6/2 and YAC128 models of Huntington's disease

Huntington's disease (HD) is an autosomal dominantly inherited progressive neurodegenerative disease. The exact sequel of events finally resulting in neurodegeneration is only partially understood and there is no established protective treatment so far. Some lines of evidence speak for the contribution of oxidative stress to neuronal tissue damage. The fumaric acid ester dimethylfumarate (DMF) is a new disease modifying therapy currently in phase III studies for relapsing-remitting multiple sclerosis. DMF potentially exerts neuroprotective effects via induction of the transcription factor “nuclear factor E2-related factor 2” (Nrf2) and detoxification pathways. Thus, we investigated here the therapeutic efficacy of DMF in R6/2 and YAC128 HD transgenic mice which mimic many aspects of HD and are characterized by an enhanced generation of free radicals in neurons. Treatment with DMF significantly prevented weight loss in R6/2 mice between postnatal days 80–90. At the same time, DMF treatment led to an attenuated motor impairment as measured by the clasping score. Average survival in the DMF group was 100.5 days vs. 94.0 days in the placebo group. In the histological analysis on day 80, DMF treatment resulted in a significant preservation of morphologically intact neurons in the striatum as well as in the motor cortex. DMF treatment resulted in an increased Nrf2 immunoreactivity in neuronal subpopulations, but not in astrocytes. These beneficial effects were corroborated in YAC128 mice which, after one year of DMF treatment, also displayed reduced dyskinesia as well as a preservation of neurons. In conclusion, DMF may exert beneficial effects in mouse models of HD. Given its excellent side effect profile, further studies with DMF as new therapeutic approach in HD and other neurodegenerative diseases are warranted.

Signal transducer and activator of transcription 3-mediated regulation of miR-199a-5p links cardiomyocyte and endothelial cell function in the heart: a key role for ubiquitin-conjugating enzymes

AIMS

Mice with a cardiomyocyte (CM)-restricted knockout of signal transducer and activator of transcription 3 (STAT3-KO) develop spontaneous heart failure. We investigated the impact of STAT3-mediated regulation of microRNAs for pathophysiological alterations in the heart.

METHODS AND RESULTS

MicroRNAchip and qRT-PCR analysis revealed elevated cardiac expression of miR-199a in STAT3-KO mice. Lentiviral shRNA-mediated STAT3-knock-down in neonatal rat CMs markedly increased miR-199a promoter activity and miR-199a levels indicative of a suppressive effect of STAT3 on miR-199a transcription. Up-regulated miR-199a in CM by pre-miR-199a transfection (pre-miR-199a-CM) reduced expression of components of the ubiquitin-proteasome system (UPS), i.e. the ubiquitin-conjugating enzymes Ube2g1 (mRNA and protein) and Ube2i (protein). Pre-miR-199a-CM or CM with siRNA-mediated down-regulation of Ube2i and Ube2g1 (siRNA-Ube2i/2g1-CM) displayed massive down-regulation of α- and β-myosin heavy chain expression associated with disrupted sarcomere structures. In addition, protein arginine methyltransferase I (PRMT-I) expression and asymmetric dimethylarginine (ADMA) synthesis were increased in pre-miR-199a-CM or in siRNA-Ube2i/2g1-CM. Increased ADMA in cell culture supernatant (SN) from pre-miR-199a-CM or siRNA-Ube2i/2g1-CM lowered nitric oxide (NO) bioavailability of rat cardiac endothelial cells while lowering ADMA concentration in CM SNs by the PRMT inhibitor arginine methyltransferase inhibitor 1 (AMI-1) (100 µM) improved NO bioavailability. In STAT3-KO hearts Ube2i and Ube2g1 expression were markedly reduced. Human terminal failing hearts harbouring low STAT3 protein levels displayed increased miR-199a levels and decreased Ube2g1 expression.

CONCLUSION

This study identifies a novel pathophysiological circuit in the heart between reduced STAT3 protein levels, increased miR-199a expression, and subsequent impairment of the UPS that disrupts CM sarcomere structure and impairs via the release of ADMA endothelial cell function.

First appraisal of brain pathology owing to A30P mutant alpha-synuclein

Familial Parkinson disease (PD) due to the A30P mutation in the SNCA gene encoding alpha-synuclein is clinically associated with PD symptoms. In this first pathoanatomical study of the brain of an A30P mutation carrier, we observed neuronal loss in the substantia nigra, locus coeruleus, and dorsal motor vagal nucleus, as well as widespread occurrence of alpha-synuclein immunopositive Lewy bodies, Lewy neurites, and glial aggregates. Alpha-synuclein aggregates ultrastructurally resembled Lewy bodies, and biochemical analyses disclosed a significant load of insoluble alpha-synuclein, indicating neuropathological similarities between A30P disease patients and idiopathic PD, with a more severe neuropathology in A30P carriers.

Variation in genes of the epidermal differentiation complex in German atopic dermatitis patients

The filaggrin (FLG) gene is one of the most widely replicated susceptibility genes for atopic dermatitis (AD) so far. Yet, FLG mutations cannot fully account for the original linkage peak on chromosome 1q21, a region comprising the so-called epidermal differentiation complex (EDC). Since the EDC contains numerous genes relevant for epidermal differentiation, we sought to evaluate variation in other genes located in this region in a German AD case-control cohort. Thirty-two single nucleotide polymorphisms (SNPs) in 21 genes across the EDC were genotyped in 402 unrelated AD patients and 325 non-atopic controls by means of restriction enzyme digestion or TaqMan assays. Allele and genotype frequencies were tested for differences between patients and controls by logistic regression. Haplotype frequencies were evaluated using the famhap software. Except for the already known association with FLG, we did not identify any additional significant associations of EDC genes with AD. Thus, in this German cohort, there is no evidence that additional genes in the EDC region apart from FLG contribute substantially to AD pathogenesis.

Unintended spread of a biosafety level 2 recombinant retrovirus

Background

Contamination of vertebrate cell lines with animal retroviruses has been documented repeatedly before. Although such viral contaminants can be easily identified with high sensitivity by PCR, it is impossible to screen for all potential contaminants. Therefore, we explored two novel methods to identify viral contaminations in cell lines without prior knowledge of the kind of contaminant.

Results

The first hint for the presence of contaminating retroviruses in one of our cell lines was obtained by electron microscopy of exosome-like vesicles released from the supernatants of transfected 293T cells. Random amplification of particle associated RNAs (PAN-PCR) from supernatant of contaminated 293T cells and sequencing of the amplicons revealed several nucleotide sequences showing highest similarity to either murine leukemia virus (MuLV) or squirrel monkey retrovirus (SMRV). Subsequent mass spectrometry analysis confirmed our findings, since we could identify several peptide sequences originating from monkey and murine retroviral proteins. Quantitative PCRs were established for both viruses to test currently cultured cell lines as well as liquid nitrogen frozen cell stocks. Gene fragments for both viruses could be detected in a broad range of permissive cell lines from multiple species. Furthermore, experimental infections of cells negative for these viruses showed that both viruses replicate rapidly to high loads. We decided to further analyze the genomic sequence of the MuLV-like contaminant virus. Surprisingly it was neither identical to MuLV nor to the novel xenotropic MuLV related retrovirus (XMRV) but showed 99% identity to a synthetic retrovirus which was engineered in the 1980s.

Conclusion

The high degree of nucleotide identity suggests unintended spread of a biosafety level 2 recombinant virus, which could also affect the risk assessment of gene-modified organisms released from contaminated cell cultures. The study further indicates that both mass spectrometry and PAN-PCR are powerful methods to identify viral contaminations in cell lines without prior knowledge of the kind of contaminant. Both methods might be useful tools for testing cell lines before using them for critical purposes.

Variation in the IL7RA and IL2RA genes in German multiple sclerosis patients

Variation in the genes encoding the interleukin (IL) 7 and IL2 receptor alpha chains (IL7RA, IL2RA) was recently found associated with multiple sclerosis (MS). We evaluated the role of these two genes in a large German MS case-control cohort. Five single nucleotide polymorphisms (SNPs) in IL7RA and four in IL2RA were genotyped in 1319 MS patients and 908 controls by means of restriction enzyme digestion or TaqMan assays and subsequently evaluated for association with MS. IL7RA expression was measured via quantitative real time PCR in 24 subjects. We replicated the association of exon 6 variation (rs6897932) in IL7RA with MS. Yet, this association was only found in patients with primary progressive (pp) or secondary progressive (sp) disease course (p=0.0004). Expression analysis did not show differences in IL7RA expression depending on genotypes at this locus, while reduced expression of the soluble receptor was observed in patients with pp and sp MS irrespective of genotype. In the IL2RA gene, significant associations of SNPs in introns 3 and 7 with MS subtypes were obvious. Together these results confirm involvement of polymorphisms in the IL7RA and IL2RA genes in MS pathogenesis and suggest that IL7RA variation may primarily affect chronic disease courses.

No evidence of an association between polymorphisms in the IRAK-M gene and atopic dermatitis in a German cohort

Atopic dermatitis (AD) is a chronic inflammatory skin disease which affects up to 10-15% of the human population in industrialized countries. A complex interaction of genetic and environmental factors is suggested to be involved in the pathogenesis of this disease. Activation of the innate immune system via toll-like receptors (TLRs) might play a role in this respect. Interleukin-1 receptor associated kinase M (IRAK-M) negatively regulates TLR signalling and inflammation. Recently, the IRAK-M gene was identified to confer linkage to asthma on chromosome 12q13-24 in a Sardinian population, and variation within the IRAK-M gene was associated with early-onset persistent asthma in Sardinian and Italian cohorts. In order to evaluate the possible role of polymorphisms in the IRAK-M gene in the pathogenesis of AD, we investigated six single nucleotide polymorphisms (SNPs) in this gene in a German AD case-control study. Unrelated AD patients (n=361) and healthy controls (n=325) were studied genetically using PCR-coupled methods. Analysis of single SNPs and haplotypes did not reveal a significant association between polymorphisms in the IRAK-M gene and AD in this cohort.

Characterization of connexin31.1-deficient mice reveals impaired placental development

The gap junction gene Connexin31.1 has been reported to be expressed predominantly in the epidermis of murine skin. To study the function of this gene, we generated mice in which the coding DNA of the Connexin31.1 gene was replaced by lacZ reporter coding DNA. Using beta-galactosidase staining, we have shown that lacZ/Connexin31.1 was expressed in the spinous and granular layers of the epidermis, in cells of olfactory epithelium and in the vomeronasal organ. During embryogenesis, Connexin31.1 was co-expressed with another isoform, Connexin31, in the post-implantation trophoblast cell lineage and, later in gestation, in placental glycogen cells. Although homozygous Connexin31.1-deficient mice were fertile and showed no morphological or functional defects in adult organs expressing this gene, 30% of the offspring expected according to Mendelian inheritance were lost between embryonic days 11.5 and 14.5 and surviving embryos were significantly reduced in weight near the end of pregnancy. Placentas of Connexin31.1-deficient embryos were reduced in weight and showed altered morphology of the spongiotrophoblast and labyrinth layer. The spongiotrophoblast formed a compact barrier at the decidual border that might restrict the maternal blood supply. We conclude that Connexin31.1 is critical for normal placental development but appears to be functionally compensated by other connexin isoforms in the embryo proper and adult mouse.

Polymorphisms in NACHT-LRR (NLR) genes in atopic dermatitis

Atopic dermatitis (AD) is a chronic skin disease affecting up to 15% of children in industrialized countries. AD belongs to the group of atopic disorders characterized by excessive immune reactions to ubiquitous antigens. Complex interactions between genetic and environmental factors have been suggested for atopic disorders. Dysregulation of the innate immune system appears crucial for the pathogenesis of AD. The NACHT-LRRs (NLRs) represent a group of innate immune receptors with special relevance for inflammatory processes. In order to investigate the role of variation in NLR genes for AD, we genotyped 23 single nucleotide polymorphisms (SNPs) in seven selected NLR genes (CARD4, CARD15, CARD12, NALP1, NALP3, NALP12, MHC2TA) in 392 AD patients and 297 controls by restriction enzyme digestion or TaqMan assays. Single-SNP analysis demonstrated significant associations of the CARD15_R702W variation and the NALP12_In9 T-allele with AD (P = 0.008 and P = 0.03, resp.; insignificant after Bonferroni correction). In the CARD4 gene, a rare haplotype was more frequent in AD patients than in controls. Interactions between all pairs of SNPs in the seven genes were analysed by logistic regression. Significant interactions comprised SNPs in the CARD4 gene (CARD4_In1 and CARD4_Ex6, P = 6.56 x 10(-7); CARD4_Prom und CARD4_Ex6, P = 2.45 x 10(-4)) and promoter polymorphisms in the CARD12 and NALP1 genes (P = 4.31 x 10(-4)). In conclusion, variation in individual genes from the NLR family as well as interactions within this group of innate immune receptor genes could play a role in AD pathogenesis. Investigations in other populations and functional studies are warranted to clarify contributions of NLR variation for this frequent skin disease.

Localization of the pannexin1 protein at postsynaptic sites in the cerebral cortex and hippocampus

Pannexins (Panx) constitute a new family of gap junction type proteins. Functional expression in paired Xenopus oocytes indicated that pannexins are capable of forming communicating junctions but also proved to be active in forming of unopposed hemichannels. In the vertebrate brain pannexins have been found in neurons. However, the subcellular cerebral localization of pannexin proteins which could gain first clues on their putative function is essentially unknown. Here we demonstrate by light and electron microscopical immunohistochemistry that Panx1 reveals postsynaptic localization in rodent hippocampal and cortical principal neurons accumulating at postsynaptic densities. The postsynaptic localization was corroborated by co-localization of Panx1 with postsynaptic density protein 95 (PSD-95), a prominent postsynaptic scaffolding protein, in hippocampal neurons expressing tagged versions of these proteins. The asymmetric synaptic distribution of Panx1 suggests that it may function in neurons as non-junctional channels (pannexons) at postsynaptic sites and comprises a novel component of the postsynaptic protein complex.

Haplotype-defined linkage region for gPRA in Schapendoes dogs

PURPOSE

In order to determine the molecular basis of canine generalized progressive retinal atrophy (gPRA), we initiated whole-genome scanning for linkage in gPRA-informative pedigrees of the Schapendoes breed.

METHODS

Detailed pedigree and ophthalmological data were assembled in selected Schapendoes pedigrees. A whole-genome scan was initiated by two-point linkage analysis using microsatellite markers in combination with haplotype analyses. Mutation screening was carried out in respective candidate genes by DNA sequencing of amplified products and quantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

Genotyping data of the microsatellite genome scan evidenced a peak two-point lod score of 4.78 for marker REN93E07 on CFA20. Haplotype analyses inferred the gPRA locus in a 5.6 megabase (Mb) region between markers FH3358 and TL336MS. Mutation screening in the genes CACNA2D3, HT017, and WNT5A revealed no causative sequence deviations. In addition, CACNA2D3 mRNA levels were equivalent in retinas of affected and healthy dogs.

CONCLUSIONS

By genome-wide linkage analysis a region for gPRA was identified and fine-localized in Schapendoes dogs. Although the mutation causing gPRA in Schapendoes dogs has not yet been identified, we established indirect DNA testing for gPRA in this breed based on linkage analysis data.

Cellular and subcellular localization of Huntington aggregates in the brain of a rat transgenic for Huntington disease

Huntington disease (HD) is a progressive neurodegenerative disorder characterized by emotional, cognitive, and motor dysfunctions. Aggregation of huntingtin is a hallmark of HD and, therefore, a crucial parameter for the evaluation of HD animal models. We investigated here the regional, cellular, and subcellular distribution of N-terminal huntingtin aggregates and associated neuropathological changes in the forebrain of a rat transgenic for HD (tgHD). The tgHD rat brain showed enormously enlarged lateral ventricles and a similar atrophy of cortical and subcortical areas as known in HD patients. Huntingtin aggregates of varying size and forms were regionally identified in neuronal nuclei, cytoplasm, dendrites, dendritic spines, axons, and synaptic terminals, closely resembling the results described earlier for human HD brains and in established HD mouse models. Huntingtin aggregates in mitochondria support mitochondrial dysfunction as contributing to the disease pathogenesis. Dark cell degeneration was reminiscent of results in HD individuals and HD mouse models. Interestingly, huntingtin aggregates were especially well accumulated in two interacting limbic forebrain systems, the ventral striatopallidum and the extended amygdala, which may contribute to the early onset of emotional changes observed in the tgHD rat. In conclusion, the tgHD rat model reflects to a remarkable extent the cellular and subcellular neuropathological key features as observed in human HD and HD mouse brains and hints of changes in limbic forebrain systems, which may elucidate the emotional dysfunction in the tgHD rat and affective disturbances in HD patients.

Degeneration of ingestion-related brainstem nuclei in spinocerebellar ataxia type 2, 3, 6 and 7

Dysphagia, which can lead to nutritional deficiencies, weight loss and dehydration, represents a risk factor for aspiration pneumonia. Although clinical studies have reported the occurrence of dysphagia in patients with spinocerebellar ataxia type 2 (SCA2), type 3 (SCA3), type 6 (SCA6) and type 7 (SCA7), there are neither detailed clinical records concerning the kind of ingestive malfunctions which contribute to dysphagia nor systematic pathoanatomical studies of brainstem regions involved in the ingestive process. In the present study we performed a systematic post mortem study on thick serial tissue sections through the ingestion-related brainstem nuclei of 12 dysphagic patients who suffered from clinically diagnosed and genetically confirmed spinocerebellar ataxias assigned to the CAG-repeat or polyglutamine diseases (two SCA2, seven SCA3, one SCA6 and two SCA7 patients) and evaluated their medical records. Upon pathoanatomical examination in all of the SCA2, SCA3, SCA6 and SCA7 patients, a widespread neurodegeneration of the brainstem nuclei involved in the ingestive process was found. The clinical records revealed that all of the SCA patients were diagnosed with progressive dysphagia and showed dysfunctions detrimental to the preparatory phase of the ingestive process, as well as the lingual, pharyngeal and oesophageal phases of swallowing. The vast majority of the SCA patients suffered from aspiration pneumonia, which was the most frequent cause of death in our sample. The findings of the present study suggest (i) that dysphagia in SCA2, SCA3, SCA6 and SCA7 patients may be associated with widespread neurodegeneration of ingestion-related brainstem nuclei; (ii) that dysphagic SCA2, SCA3, SCA6 and SCA7 patients may suffer from dysfunctions detrimental to all phases of the ingestive process; and (iii) that rehabilitative swallow therapy which takes specific functional consequences of the underlying brainstem lesions into account might be helpful in preventing aspiration pneumonia, weight loss and dehydration in SCA2, SCA3, SCA6 and SCA7 patients.

Association screen for atopic dermatitis candidate gene regions using microsatellite markers in pooled DNA samples

Atopic dermatitis (AD) is a chronic inflammatory skin disease affecting up to 16% of children in developed countries. A complex genetic background for AD has been suggested, with genetic as well as environmental factors influencing disease susceptibility. Among other factors, dysregulation in both the innate and the adaptive immune system has been proposed to play a role in AD pathophysiology. We present here an extended association screen for AD using microsatellite markers in 154 genes related to innate and adaptive immunity in pooled DNA samples from 150 German children with AD and 100 controls. After Bonferroni correction, no marker revealed a significant association with AD. Yet, markers representing the nuclear factor kappa B (NFKB)1 and chemokine receptor (CCR)4 genes showed differences in allelic distributions between cases and controls for both pooled DNA analysis and individual genotyping and were thus further investigated. Evaluation of additional single nucleotide polymorphisms (SNP) in the NFKB1 and CCR4 genes revealed no association of individual SNPs with AD. In contrast, haplotype analyses showed a significantly different haplotype distribution between patients and controls for CCR4 (P < 0.001). Furthermore, when SNP-SNP interaction effects were analysed for these two genes, we found significant evidence for epistatic interactions between SNPs within each of the two genes but no evidence for a gene-gene interaction, suggesting that variation in or near both the CCR4 and the NFKB1 genes might individually contribute to AD pathogenesis.

Behavioral abnormalities precede neuropathological markers in rats transgenic for Huntington's disease

Huntington's disease (HD) is caused by an expanded CAG repeat leading to the synthesis of an aberrant protein and to the formation of polyglutamine (polyQ)-containing inclusions and aggregates. Limited information is available concerning the association of neuropathological markers with the development of behavioral markers in HD. Using a previously generated transgenic rat model of HD (tgHD rat), we performed association studies on the time-course of behavioral symptoms (motor function, learning, anxiety) and the appearance of striatal atrophy, 1C2 immunopositive aggregates and polyQ recruitment sites, a precursor to these aggregates. At the age of 1 month, tgHD rats exhibited reduced anxiety and improved motor performance, while at 6 months motor impairments and at 9 months cognitive decline occurred. In contrast, polyQ recruitment sites appeared at around 6-9 months of age, indicating that HD-like behavioral markers preceded the appearance of currently detectable neuropathological markers. Interestingly, numerous punctate sites containing polyQ aggregates were also seen in areas receiving afferents from the densely recruiting regions suggesting either transport of recruitment-competent aggregates to terminal projections where initially 1C2 positive aggregates were formed or different internal properties of neurons in different regions. Furthermore, striatal atrophy was observed at the age of 12 months. Taken together, our findings support the hypothesis of a dynamic process leading to region- and age-specific polyQ recruitment and aggregation. The dissociation of onset between behavioral and neuropathological markers is suggestive of as yet undetected processes, which contribute to the early phenotype of these HD transgenic rats.

Cellular and subcellular localization of paralemmin-1, a protein involved in cell shape control, in the rat brain, adrenal gland and kidney

Paralemmin-1 is a phosphoprotein, lipid-anchored to the cytoplasmic face of membranes and implicated in plasma membrane dynamics and cell process formation. We report an immunoperoxidase histochemical analysis of the cellular and subcellular localization of paralemmin-1 in the rat tissues where its expression is highest: the brain, the adrenal gland and the kidney. Paralemmin-1 is detected throughout the brain, in neuronal perikarya, axons and dendrites including dendritic spines and also in glial processes. In the adrenal gland, paralemmin-1 is highly expressed in the medulla. The kidney displays a pattern of differential paralemmin-1 expression in various structures and cell types, with high concentrations in cells of the parietal epithelium of Bowman's capsule, intermediate tubules, distal tubules and principal cells of outer medullary collecting ducts. Mosaics of paralemmin-positive and paralemmin-negative cells are observed in proximal tubules, the parietal epithelium of Bowman's capsule and the endothelium of many blood vessels. Plasma membrane association in epithelia is often polarized: paralemmin-1 concentrates at the apical membranes of adrenal chromaffin cells, but at the basolateral plasma membranes of proximal and distal tubule cells in the kidney. Paralemmin-1 immunoreactivity exhibits a spotted pattern and can be seen both at plasma membranes and within the cytoplasm, where it is often associated with endomembranes. This discontinuous distribution and the detergent extraction properties of paralemmin-1 suggest an association with lipid microdomains. The findings are consistent with a role for paralemmin-1 in the formation and stabilization of plasma membrane elaborations, in neurons as well as in other cell types.

Molecular characterization and immunohistochemical localization of palmdelphin, a cytosolic isoform of the paralemmin protein family implicated in membrane dynamics

Palmdelphin is a newly identified cytosolic isoform of paralemmin-1, a lipid raft-associated protein implicated in cell shape control. Like paralemmin-1, palmdelphin is phosphorylated, giving rise to electrophoretic band heterogeneity that is most pronounced in the brain. In ultracentrifugation and gel filtration palmdelphin behaves as a non-globular monomer. Its C-terminal region binds glutamine synthetase. Immunohistochemical analysis of the rat brain shows a prominent localization of palmdelphin in the cerebral cortex, hippocampus, amygdala, septum, indusium griseum, piriform cortex, nucleus supraopticus, and nucleus of the lateral olfactory tract. Many of the circumscript palmdelphin-positive areas are related to the olfactory system. Immunoperoxidase electron microscopy reveals a discontinuous distribution of palmdelphin immunoreactivity, in the form of spots scattered throughout the cytoplasm of selected neuronal perikarya and dendrites, including dendritic spines, often in association with endomembranes, and in a pattern which is similar to that of the cytoplasmic fraction of paralemmin-1. In subcellular fractionation experiments palmdelphin behaves as a cytosolic protein which, however, can be partially recruited from cytosol to the detergent-resistant fraction of a membrane/cytoskeletal cell ghost preparation. These observations suggest that palmdelphin may peripherally associate with endomembranes or cytoskeleton-linked structures.

Evaluation of the toll-like receptor 6 Ser249Pro polymorphism in patients with asthma, atopic dermatitis and chronic obstructive pulmonary disease

Background

For allergic disorders, the increasing prevalence over the past decade has been attributed in part to the lack of microbial burden in developed countries ('hygiene hypothesis'). Variation in genes encoding toll-like receptors (TLRs) as the receptor system for the first innate immune response to microbial stimuli has been implicated in various inflammatory diseases. We evaluated here the role of a coding variation, Ser249Pro, in the TLR6 gene in the pathogenesis of asthma, atopic dermatitis (AD) and chronic obstructive pulmonary disease (COPD).

Methods

Genotyping of the Ser249Pro polymorphism in 68 unrelated adult patients and 132 unrelated children with asthma, 185 unrelated patients with COPD, 295 unrelated individuals with AD and 212 healthy control subjects was performed by restriction enzyme digestion.

Results

We found a weak association of the 249Ser allele with childhood asthma (p = 0.03). Yet, significance was lost after Bonferroni correction. No association was evident for AD or COPD.

Conclusion

Variation in TLR6 might play a role in the pathogenesis of childhood asthma.

Loss of connexin36 increases retinal cell vulnerability to secondary cell loss

Accruing evidence indicates that gap junctions are involved in neuronal survival after brain injury. The present study was aimed at clarifying the contribution of the neuronal gap-junction protein connexin36 (Cx36) to secondary cell loss after injury in the mouse retina. A focal retinal lesion was induced by infrared laser photocoagulation. Remarkably, this model allowed spatial and temporal definition of the lesion with high reproducibility. Moreover, Cx36 is abundantly expressed in the retina and plays an essential role in the visual transmission process. Taking advantage of these features, cell death was assessed using TUNEL assay and light and electron microscopy, and the extent of Cx36 expression was studied by immunohistochemistry, Western blot, in situ hybridization and real-time RT-PCR. Secondary cell loss was most prominent between 24 and 48 h after lesioning. This peak was accompanied by an increase in Cx36 expression. When cultured explanted retinas were subjected to gap-junction blockers a significant increase in the extent of secondary cell loss after laser photocoagulation became evident. Using the same experimental paradigm we compared the incidence of cell death in wild-type and Cx36(-/-) mice. A significant increase in total number of TUNEL-positive cells occurred in the Cx36(-/-) mice compared to controls. From these data we conclude that Cx36 contributes to the survival and resistance against damage of retinal cells and thus constitutes a protective factor after traumatic injury of the retina.

Fine-structural analysis and connexin expression in the retina of a transgenic model of Huntington's disease

Recent studies indicate that the visual system appears more frequently affected in polyglutamine diseases than expected previously. Here, we investigated retinal degenerations in adult transgenic R6/2 mice, a model for Huntington's disease (HD). Light microscopical analysis revealed retinal dystrophy all over the retina, with central areas showing major effects. Electron microscopical analysis showed strong degenerations of outer and inner photoreceptor segments, shrinkage of photoreceptor cell somata, and signs of degeneration in photoreceptor terminals in the outer plexiform layer. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling showed hints of apoptosis. Mutant huntingtin and ubiquitin were expressed in all classes of retinal neurons, the pigment epithelium, and to a minor extent in neuropil structures. For investigating possible links to functional impairments in the rod-cone pathway, expression levels of three connexins (Cx) were compared in R6/2 and wildtype mice retinae. In R6/2 mice, expression of Cx36, the major neuronal connexin in the retina, was slightly reduced in the outer plexiform layer, indicating affected photoreceptor terminals as detected at the electron microscopical level. In contrast, Cx45, a putative neuronal connexin in the retina, was remarkably reduced in the inner plexiform layer of R6/2 mice. This result corresponded to fainter signals of Cx45 mRNA as documented by in situ hybridization and to a lower level of mCx45 cDNA as obtained by polymerase chain reaction after reverse transcription, suggesting functional deficits in spatial processing of Cx45-mediated gap junction coupling due to transgene-induced retinal degenerations. Thus, it is important to clarify the meaning of visual involvement in HD.